A large portion of the metallic alloys in use today are processed by solidification casting, at least initially. The metallic alloy is melted and cast into a metal or ceramic mold, where it solidifies. The mold is stripped away, and the cast metallic piece is ready for use or further processing. The as-cast structure of most materials produced during solidification and cooling depends upon the cooling rate. There is no general rule for the nature of the variation, but for the most part the structure changes only gradually with changes in cooling rate. On the other hand, for the bulk-solidifying amorphous alloys the change between the amorphous state produced by relatively rapid cooling and the crystalline state produced by relatively slower cooling is one of kind rather than degree—the two states have distinct properties.
Bulk-solidifying amorphous alloys, or bulk metallic glasses (“BMG”), are a recently developed class of metallic materials. These alloys may be solidified and cooled at relatively slow rates, and they retain the amorphous, non-crystalline (i.e., glassy) state at room temperature. This amorphous state can be highly advantageous for certain applications. If the cooling rate is not sufficiently high, crystals may form inside the alloy during cooling, so that the benefits of the amorphous state are lost. For example, one risk with the creation of bulk amorphous alloy parts is partial crystallization due to either slow cooling or impurities in the raw material. Thus, ensuring a high degree of amorphicity (and, conversely, a low degree of crystallinity) can be important in the quality control of a BMG fabrication process.
Currently, the methods to measure the degree of crystallinity can include bending test, x-ray radiography, and etching. These pre-existing techniques are destructive to the measurement specimens. The most common current method for screening relies on either a destructive strength test, or sectioning and subsequent visual screening for crystallization. As a result, for a BMG part (e.g., a casing) that needs to be measured for its degree of crystallinity, it needs to first be significantly altered (e.g., sectioned, published, and/or ground to a powder form).
Thus, a need exists to develop methods that can provide a measurement of the degree of crystallinity (and thus, the amorphous content) of a BMG accurately and automatically, thereby facilitating a more rapid and cost efficient quality control of its fabrication process.